The objectives of the research are to determine the importance and impact of spatial and temporal variation of soil hydraulic properties on calculated runoff volumes. The study also addresses the importance of storm frequency and its relationship to rainfall/runoff processes and spatial variation of soil hydraulic properties. A pedo-transfer function, based on soil physical properties, was developed to predict the variation of antecedent moisture content (AMC) with increasing time between storm events. The effective hydraulic conductivity (Keff) was evaluated at a value of half the calculated saturated hydraulic conductivity. The AMC was varied for three different scenarios on 7 individual soil surfaces located within a 228 km2 (88 mi2) arid watershed in the Mojave Desert. The modeling software packages used for the study were Rosetta, HYDRUS-1D, and FLO-2D. All data were geospatially rectified on the watershed (using ArcGIS) to account for the spatial variation of the soil parameters. Temporal variation of water content on each soil surface was evaluated using atmospheric demand and the soil properties over a 5-day period. The results show that the spatial variability of Ks and AMC have considerable effect on predicted flowrates due to varied precipitation and varied soil water content, which for the upper watershed were shown to increase as storm frequency decreases (i.e., return interval increases). As the drying time increases from 1 to 5 days, the calculated runoff reduces 46 percent (at the upper watershed) for the 100-year models. The model shows that the floodwave from upstream does progress to the outfall for the 500-year event; however, the majority of run-on and runoff infiltrates on the lower portion of the watershed for the 100-year and higher frequency events.